Peopel atatch childseats to the luggageblock, and ask how many overloaded the T bag. He is not going to jump curbs with the dog in. Take a look at Flickr what peopel hang on the luggageblock.

Edit: http://www.practicalcycles.com/userimages/procart27.htm

Front Cargo Carrier Flat Bed

@ Ekdog: do you have other options than the Brompton for this?